1. Field of the Invention
This invention relates generally to a telecommunication system, and, more particularly, to a wireless telecommunication system.
2. Description of the Related Art
In conventional wireless telecommunications, one or more mobile units may establish a wireless link to a Radio Access Network (RAN). The RAN architecture is typically hierarchical and call state information associated with each mobile unit call session is stored in a central repository, such as a Radio Network Controller (RNC), a Packet Data Serving Node (PDSN), and the like. If the user of the mobile unit changes geographical location while the mobile unit is dormant, a paging process may be used to locate the mobile unit. For example, the paging process may be initiated when data intended for the mobile unit arrives at a radio network controller. Upon receiving the page, the mobile unit may transmit an identifier, such as a Unicast Access Terminal Identifier (UATI), which may be used to locate the appropriate call state information in the central repository. The mobile unit may also re-activate the dormant session, in which case the UATI is transmitted and used to locate the appropriate call state information in the central repository.
One alternative to the conventional hierarchical network architecture is a distributed architecture including a network of base station routers. For example, each base station router may combine RNC and/or PDSN functions in a single entity that manages radio links between one or more mobile units and an outside network, such as the Internet. Compared to hierarchical networks, distributed architectures have the potential to reduce the cost and/or complexity of deploying the network, as well as the cost and/or complexity of adding additional wireless access points, e.g. base station routers, to expand the coverage of an existing network. Distributed networks may also reduce (relative to hierarchical networks) the delays experienced by users because packet queuing delays at the RNC and PDSN of hierarchical networks may be reduced or removed.
In a distributed architecture, one or more mobile units may establish a call session with any one of the plurality of base station routers. Accordingly, each base station router should be capable of assigning an identifier, such as a UATI, to the mobile unit. For example, a proposed Code Division Multiple Access (CDMA) protocol standard, sometimes referred to as the EVolution-Data Only (EVDO) standard, specifies a unique 128-bit UATI that is assigned to a mobile unit when a call session is initiated by the mobile unit. The mobile unit maintains the UATI for the duration of the call session. In the current implementation, the EVDO call session UATI is divided into two parts: a 104-bit UATI104 and a 24-bit UATI024. The UATI024 portion is unique to the mobile unit for the duration of the call session and the UATI104 is common to all mobile units within a predetermined subnet of base station routers in the distributed network.
In operation, base station routers in a conventional distributed network broadcast, or advertise, their subnet address, e.g. the address indicated by the UATI104 portion of the UATI. However, the address is generally too long to advertise on a control channel, so the base station routers advertise an 8-bit alias to the subnet address called a color code. Mobile units may then determine whether or not the subnet including the base station router providing service to the mobile unit has changed by monitoring the advertised color code on the control channel. If the mobile unit detects a change in the color code, the mobile unit is typically required to request a new UATI. For example, a mobile unit may initiate a call session with a first base station router belonging to a first subnet having a first color code. The first base station router assigns a UATI to the mobile unit. If the mobile unit becomes dormant and later re-activates by sending a message to a second base station router belonging to a second subnet having a second color code, the mobile unit should request a new UATI from the second base station router.
However, the base station routers may have difficulty locating call session information associated with the dormant call session when the dormant mobile unit is re-activated. For example, after a mobile unit may initiate a call session with a first base station router, the mobile unit may be handed off to a second base station router, which may also receive and store the associated call state information. If the mobile unit then becomes dormant and later re-activates by sending a message to a third base station router, the third bas station router may not be able to locate the call session information stored on the second base station router.
The present invention is directed to addressing the effects of one or more of the problems set forth above.